Carbon Molecular Sieve Research Articles

Uncovering the potential of MSC CT-350 for CO2/CH4 separation toward the optimization of a Pressure Swing Adsorption process for biogas upgrading

A laboratory-scale fixed-bed column is employed to study the dynamic behavior of the carbon molecular sieve MSC CT-350 for CO2/CH4 separation. Breakthrough adsorption tests in single-component systems are carried out at different pressures (1, 3, 5, 6.5 and 8 bar) and constant temperature (20 °C). Moreover, an additional test is conducted with a 40% CO2/60% CH4 binary mixture at 3 bar. Desorption tests are performed by varying the purge-to-feed ratio (P/F) at 50%, 30% and 20%, optionally using a vacuum pump. Experimental results show that MSC CT-350 has a good CO2 adsorption capacity for each pressure, considerably higher than CH4. In the binary test, very slight differences are experimentally found in the adsorption kinetics and equilibrium adsorption capacity with respect to single-compound tests, which results equal to 2.16 mol kg−1 for CO2 and 0.302 mol kg−1 for CH4 at 3 bar, compared with 2.29 mol kg−1 for CO2 and 0.262 mol kg−1 for CH4 for the single-compoound counterparts. The time required for a complete regeneration decreases with the increase in purge flowrate and with the simultaneous use of the vacuum pump. Finally, CO2 adsorption is a reversible process as the CO2 adsorption capacity of the adsorbent is not significantly reduced when utilized in subsequent adsorption-desorption cycles.

Study on the lignin-derived sp2–sp3 hybrid hard carbon materials and the feasibility for industrial production

Hard carbon has been widely used in anode of lithium/sodium ion battery, electrode of supercapacitor, and carbon molecular sieve for CO2 capture and hydrogen storage. In this study the lignin derived hard carbon products are investigated, and the conclusions are abstracted as follows. (1) The lignin derived hard carbon products consist of microcrystal units of sp2 graphene fragments, jointed by sp3 carbon atoms and forming sp2–sp3 hybrid hard carbon family. (2) From the lignin precursors to the sp2–sp3 hybrid hard carbon products, most carbon atoms retain their original electron configurations (sp2 or sp3) and keep their composition in lignin. (3) The architectures of lignin-derived hard carbon materials are closely dependent on the forms of their lignin precursors, and could be preformed by different pretreatment techniques. (4) The carbonization of lignin precursors follows the mechanism “carbonization in situ and recombination nearby”. (5) Due to the high carbon ratio and abundant active functional groups in lignin, new activation techniques could be developed for control of pore size and pore volume. In general lignin is an excellent raw material for sp2–sp3 hybrid hard carbon products, a green and sustainable alternative resource for phenolic resin, and industrial production for lignin derived hard carbon products would be feasible.

Single-Component Adsorption Equilibria of CO2, CH4, Water, and Acetone on Tapered Porous Carbon Molecular Sieves.

Engineered carbon molecular sieves (CMSs) with tapered pores, high surface area, and high total pore volume were investigated for their CO2, CH4, water, and acetone adsorption properties at 288.15, 298.15, 308.15 K, and pressures of <1 bar. The results were compared with BPL carbon. The samples exhibited higher adsorption capacity for CO2 compared to BPL carbon, with Carboxen 1005 being the highest due to the presence of ultramicropores (pores smaller than 0.8 nm). Similar observations were made for CH4 except at 288.15 K. Although the CMSs exhibited higher hydrophobicity than BPL carbon, the latter had the highest acetone uptake for all investigated temperatures due to its higher oxygen content, which facilitates stronger interactions with polar VOC molecules. Heats of adsorption were calculated using the Clausius-Clapeyron equation after fitting the isotherms with the dual-site Langmuir-Freundlich model, and results largely corroborated the order of adsorption capacities of CO2, CH4, and water on the carbon materials.

Carbon Molecular Sieve Membranes with Ultra-Thin Selective Skin Layer by Pyrolysis of Porous Hollow Fibers.

Translating carbon molecular sieve (CMS) membranes into highly scalable hollow fiber geometry with ultra-thin selective layer (<1µm) for gas separation remains as great challenge. The porous support layer of precursor hollow fiber membranes is prone to collapse during pyrolysis, which induces thick skin layer (15-50µm) of CMS hollow fiber membranes. Here, a novel strategy is present to obtain an ultra-thin selective skin layer by carbonization of hollow fiber membranes with porous skin. P84-based defect-free CMS hollow fiber membranes with ultra-thin selective skin layer (0.9µm) for gas separation are prepared without any coating or complex chemical pretreatment. Compared with the carbon membranes derived from defect-free fibers, the H2 permeance (93.9 GPU) of CMS membranes derived from the porous fibers increases ≈1353% with comparable selectivity of H2/CH4 (143) and higher H2/N2 (120). Furthermore, the porous fibers are pre-aged near the Tg in N2 conditions before carbonization, and the H2 permeance of the derived CMS hollow fiber membranes reached 147 GPU (increased 2180%). It is a new facile way to prepare CMS hollow fiber membranes with ultra-thin selective layer by porous fibers, demonstrating its versatile potential in gas separation or organic liquids separation.

In-situ crosslinking of a novel conjugated dialkynyl-based polyimide for high performance carbon molecular sieve membrane

High-performance and reliable membranes for efficient gas separation and their design strategies are key points for membrane-based carbon capture. Here, we reported a high-performance carbon membrane design protocol from a microporous, highly rigid polyimide precursor (6FBD1-CR), which was produced by in-situ crosslinking a polyimide (6FBD1) containing conjugated dialkynyl group at 300 °C. The possible crosslinking mechanisms are the [2+2+2] trimerization of three ethynyl groups to form a benzene ring and the Diels-Alder reaction between the ethynyl bond and phenylacetylene to generate the fused naphthalene ring. After crosslinking, the membrane shows a ∼ 8-fold improved microporosity (37.1–298 m2 g−1). When pyrolyzed at 550 °C, the resulting 6FBD1-CMS demonstrates very high pure- and mixed-gas separation performance. E.g., the CO2 permeability reaches 7661 Barrer and CO2/CH4 selectivity of 44, additionally, even at the CO2/CH4 mixed-gas pressure of 30 bar, the PCO2 can still reach 4920 Barrer combined with a αCO2/CH4 of 28, which is well above the latest CO2/CH4 mixed-gas Upper Bound line. We consider this is due to the acetylene crosslinking induced a very stable microporous structure composed of rigid fused rings that alleviate the micropore collapse during the carbonization process, and thus, resulting in a relatively higher BET surface area, larger d-spacing, relatively higher concentration of continuous disordered phase (higher sp3/sp2) and small activation energy (Ep) for gas transport than the CMSM derived from polyimide without pre-crosslinking. This finding provides new opportunity for the structural design of high-performance CMSMs.

Field-Scale Testing of a High-Efficiency Membrane Reactor (MR)-Adsorptive Reactor (AR) Process for H2 Generation and Pre-Combustion CO2 Capture.

The study objective was to field-validate the technical feasibility of a membrane- and adsorption-enhanced water gas shift reaction process employing a carbon molecular sieve membrane (CMSM)-based membrane reactor (MR) followed by an adsorptive reactor (AR) for pre-combustion CO2 capture. The project was carried out in two different phases. In Phase I, the field-scale experimental MR-AR system was designed and constructed, the membranes, and adsorbents were prepared, and the unit was tested with simulated syngas to validate functionality. In Phase II, the unit was installed at the test site, field-tested using real syngas, and a technoeconomic analysis (TEA) of the technology was completed. All project milestones were met. Specifically, (i) high-performance CMSMs were prepared meeting the target H2 permeance (>1 m3/(m2.hbar) and H2/CO selectivity of >80 at temperatures of up to 300 °C and pressures of up to 25 bar with a <10% performance decline over the testing period; (ii) pelletized adsorbents were prepared for use in relevant conditions (250 °C < T < 450 °C, pressures up to 25 bar) with a working capacity of >2.5 wt.% and an attrition rate of <0.2; (iii) TEA showed that the MR-AR technology met the CO2 capture goals of 95% CO2 purity at a cost of electricity (COE) 30% less than baseline approaches.

A new segment-level mixing strategy to improve the gas separation performances of carbon molecular sieve membrane derived from polymer blends

A novel mixing strategy for optimizing the structures and gas separation properties of carbon molecular sieve membranes (CMSMs) through the precise segment-level mixing of polyimide-co-siloxane (PSI) blends is proposed. PSI copolymers with different contents of siloxane were synthesized and blended, denoted as PSI-0, PSI-1, PSI-2, and PSI-3 based on the molar ratio of DABA:siloxane, 10:0, 9:1, 8:2, and 7:3, respectively. This study focuses on unraveling the intricate interplay between repeating segment distribution and resulting carbonization structures, with a specific emphasis on the gas separation performances of CMSMs. Of particular interest is the PSI-0:PSI-3 (1:2) blend, which, despite containing an identical siloxane amount to neat PSI-2, yields a CMSM with comparable hydrogen permeability and significantly enhanced selectivity (232 % H2/CH4 and 184 % H2/N2 selectivity). These findings underscore the critical role of segment distribution in achieving superior gas separation performances, presenting a promising avenue for the precise engineering of polymer precursor structures to optimize CMSM properties.

Microwave irradiation-induced alterations in physicochemical properties and methane adsorption capability of coals: An experimental study using carbon molecular sieve

In order to comprehend the applicability of microwave irradiation for recovering coalbed methane, it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism. In this work, the carbon molecular sieve combined with KMnO4 oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees, which can serve as model substances toward coals. Afterwards, the microwave irradiation dependences of pores, functional groups, and high-pressure methane adsorption characteristics of model substances were studied. The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups, which could block the micropores with a size of 0.40–0.60 nm in carbon molecular sieve; meanwhile, naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70–0.90 nm. These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%–23.28%, suggesting that microwave irradiation could promote methane desorption. Moreover, the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion. In summary, the oxidized carbon molecular sieve can act as model substances toward coals with different ranks. Additionally, microwave irradiation is a promising technology to enhance coalbed methane recovery.

Above-Tg Annealing Benefits in Nanoparticle-Stabilized Carbon Molecular Sieve Membrane Pyrolysis for Improved Gas Separation.

Nanoparticles can suppress asymmetric precursor support collapse during pyrolysis to create carbon molecular sieve (CMS) membranes. This advance allows elimination of standard sol-gel support stabilization steps. Here we report a simple but surprisingly important thermal soaking step at 400 °C in the pyrolysis process to obtain high performance CMS membranes. The composite CMS membranes show CO2 /CH4 (50 : 50) mixed gas feed with an attractive CO2 /CH4 selectivity of 134.2 and CO2 permeance of 71 GPU at 35 °C. Furthermore, a H2 /CH4 selectivity of 663 with H2 permeance of 240 GPU was achieved for promising green energy resource-H2 separation processes.

Above‐Tg Annealing Benefits in Nanoparticle‐Stabilized Carbon Molecular Sieve Membrane Pyrolysis for Improved Gas Separation

AbstractNanoparticles can suppress asymmetric precursor support collapse during pyrolysis to create carbon molecular sieve (CMS) membranes. This advance allows elimination of standard sol‐gel support stabilization steps. Here we report a simple but surprisingly important thermal soaking step at 400 °C in the pyrolysis process to obtain high performance CMS membranes. The composite CMS membranes show CO2/CH4 (50 : 50) mixed gas feed with an attractive CO2/CH4 selectivity of 134.2 and CO2 permeance of 71 GPU at 35 °C. Furthermore, a H2/CH4 selectivity of 663 with H2 permeance of 240 GPU was achieved for promising green energy resource‐H2 separation processes.

Carbon Molecular Sieve Membranes from Multiring Highly Aromatic Functional Copolymers

Carbon Molecular Sieve Membranes from Multiring Highly Aromatic Functional Copolymers

Enhancing gas separation performance of polyimide with Tröger’s bases: Unveiling the impact on polymer and carbon molecular sieve membranes

The potential of carbon molecular sieve membranes (CMSM) for gas separation is widely recognized, and the key precursor for these membranes is polyimide (PI). This study focuses on enhancing the gas separation properties of CMSMs by introducing a unique structural element, Tröger’s bases, into polyimides, resulting in the creation of five distinct polyimides containing Tröger’s bases (PI-TBs). The incorporation of Tröger’s bases has a profound impact on the arrangement of polymer chains within the PIs, leading to a substantial improvement in gas permeability without compromising selectivity. Following carbonization at 600 °C, the resultant CMSMs exhibit significantly enhanced gas permeability while preserving, and in some cases, improving gas selectivity. Among the various types of diamines considered, the 6FDA variant of PI-TB stands out, boasting outstanding gas permeability with a H2 permeability of 4991.0 Barrer and a H2/CH4 selectivity of 30.7; this level of performance surpasses the 2015 Robeson’s upper bound. Furthermore, thermal analysis coupled with mass spectrometry (TG-MS) reveals that the pyrolysis of Tröger’s bases commences prior to that of polyimide. This sequential degradation process facilitates the formation of pyridine N and promotes the π-stacking of PI chains; both of which are instrumental in maintaining excellent gas selectivity. These findings provide valuable insights into the roles of Tröger’s bases in enhancing the gas separation performance of PIs and CMSMs, offering a promising avenue for further advancements.

Techno-economic analysis of carbon molecular sieve membranes to produce oxygen enrichment air

Oxygen Enriched Air (OEA) is essential for medical applications, metal production, chemical production, the petrochemical industry, and energy processes. In this work, carbon molecular sieve membranes (CMSM) and membrane systems are analyzed concerning their technical and economic feasibility to produce OEA for medical, post-combustion, and oxy-combustion applications. Process parameters, such as stage-cut, feed-to-permeate pressure ratio, membrane area, and the number of stages, were studied to assess the technical and economic feasibility of this technology. In this work, it was observed that for each membrane, there is a permeating oxygen concentration that minimizes the specific oxygen cost. The production of 56 tonO2·day−1 for a combustion enhancement process with a concentration of 72 % was obtained in a single-stage with a specific cost of 61.0 €·tonO2−1. A single-stage is also effective for producing OEA for medical applications (required concentration of 82 %) at a minimum separation cost of 45.8 €·tonO2−1. However, a two-stage system is required to produce OEA with a concentration higher than 95 % for oxy-combustion with an OEA production cost of 83.8 €·tonO2−1. These production costs are lower than those obtained with two different commercial membranes and are competitive with medium-scale cryogenic distillation and pressure swing adsorption processes.

Influence of the coagulation bath on the nanostructure of cellulose films regenerated from an ionic liquid solution.

Cellulose membranes were prepared from an EMIMAc ionic liquid solution by nonsolvent-induced phase separation (NIPS) in coagulation baths of water-acetone mixtures, ethanol-water mixtures and water at different temperatures. High water volume fractions in the coagulation bath result in a highly reproducible gel-like structure with inhomogeneities observed by small-angle neutron scattering (SANS). A structural transition of cellulose takes place in water-acetone baths at very low water volume fractions, while a higher water bath temperature increases the size of inhomogeneities in the gel-like structure. These findings demonstrate the value of SANS for characterising and understanding the structure of regenerated cellulose films in their wet state. Such insights can improve the engineering and structural tuning of cellulose membranes, either for direct use or as precursors for carbon molecular sieve membranes.

Ағынды суларды отандық көміртек құрамды адсорбенттермен тазарту және су құрамына физика-химиялық талдау жүргізу

Various strategies are being implemented to improve water use efficiency in the face of increasing world population and increasing demand for depleting fresh water sources. Wastewater treatment and reuse are effective strategies, especially if the treated water can be reused. Water scarcity is a growing global problem caused by a combination of factors such as population growth, climate change and unsustainable water management practices.&#x0D; This article presents the results of a study in the accredited analytical laboratory of the treatment facilities of the State Industrial Complex "Astana Su Arnasy", where wastewater was treated with domestic carbon-containing adsorbents (Shubarkol, Shoptykol, humic acid, carbon molecular sieves, carbon black) and were carried out with chemical water analysis. The results of this study showed that samples obtained on the basis of carbon materials can be used as adsorbents for purifying liquid media (from suspended solids, heavy metal salts, surfactants, petroleum products, etc.).

Breaking the Permeability-Selectivity Trade-Off: Advanced carbon molecular sieve membranes derived from thermally rearranged Mixed-Matrix membrane precursors

A crucial problem in membrane-based gas separation is to fabricate membranes with excellent permeability, selectivity, and stability. Here, a high-performance carbon molecular sieves membrane of TR-CMS/SSZ-13 was successfully produced by pyrolyzing a thermally rearranged (TR) mixed matrix membrane (MMM) that obtained from a copolyimide precursor (6FDA/ODA/6FAP(3:2)) and SSZ-13 zeolite as filler at 450 °C. The effect of SSZ-13 zeolite content and structures of precursors on the transport behavior of derived CMS membranes was thoroughly studied. After TR process, the as formed polybenzoxazole (PBO) chain resulted in an enhanced rigidity, higher fractional free volume (0.15 vs 0.17), and a significantly increased (1898 times) BET surface area. Further enhancing the treatment temperature to 650 °C, the formed TR-CMS membranes exhibited a huge improved BET surface area from 228.2 to 639.3 m2/g, delivering a remarkable gas separation performance with H2 permeability of 7089 Barrer and H2/CH4 selectivity of 136. When doping with SSZ-13 till 15 wt%, the TR-CMS/SSZ-13–15 % showed an even higher H2 (9726 Barrer) and CO2 permeability (6932 Barrer), as well as H2/CH4 (150 vs 136) and CO2/CH4 (107 vs 57) selectivity than the pure TR-CMS, which surpassed the newest 2019 Robeson Upper bound. This can associate with the strong interaction between the modified SSZ-13 and the polymer matrix that prevent the collapse of the aromatic strand during the pyrolysis process, thereby create more ultra-micropore volume and concentration. Conclusively, pyrolyzing TR-MMM precursor is an effective way to form high-performance membranes with good potential for CO2 separation and H2 purification.

Directly measured pyrolysis temperature dependence of sorption selectivity for carbon dioxide/methane in Matrimid® polyimide-derived carbon molecular sieve membranes

In this study, we augment our analysis of pyrolysis temperature dependence of carbon molecular sieve (CMS) membranes derived from a polyimide, Matrimid® useful for advanced CMS membranes. Our direct sorption results prove that the strong pyrolysis temperature dependence of permselectivity for the CO2/CH4 gas pair is promoted by an unusual trend in sorption selectivity reported here. This trend complements conventional diffusion selectivity trends for this pair with increasing pyrolysis temperatures. Our results show that the elimination of pyridinic and pyrrolic groups over the same pyrolysis temperature range occurs. Elimination of such CO2-philic pyridinic and pyrrolic groups typically would be expected to cause a trend opposite to that actually measured directly for CO2/CH4 selectivity. The resulting trend for pyrolysis temperatures between 550 °C and 900 °C, however, can be explained in terms of microporous and ultramicroporous properties of the CMS for increasing pyrolysis temperatures. Specifically, apparent thermodynamic exclusion selectivity of the 0.5 Å larger CH4 vs. the slim 3.3 Å CO2 provides a consistent explanation of the trends. This discovery provides additional options to tune permselectivity of CMS membranes to complement molecular sieving based on diffusion contributions.

High-performance hydrogen separation using cellulose-based carbon molecular sieve membranes

Cellulose-based carbon molecular sieve membranes were designed for hydrogen deblending from natural gas and hydrogen recovery from other relevant industrial sources. The crystallinity of the cellulose precursor was increased by adding propylene glycol, which originated a carbon membrane with a permeability to the hydrogen of 544 barrer and an H2/CH4 permselectivity of ca. 3500 (Robeson index = 100). A careful optimization of the carbonization conditions of the cellulose precursor boosted the carbon membrane permeability to hydrogen to 1144 barrer and the H2/CH4 permselectivity to 1080 (Robeson index = 62). The membrane with the highest permeability to hydrogen presented the highest micropore volume of 0.443 cm3·g−1 and a micropore surface area of 1326 m2·g−1.A detailed techno-economic analysis of the hydrogen recovery from the natural gas was performed. It was concluded that a single-stage carbon membrane module can recover hydrogen with a concentration of 99.8 % and a specific cost of 0.26 €·kgH2−1 for a hydrogen recovery of 68 %. A two-stage membrane process was simulated to deliver a purity >99.997 % and a recovery of 96 %, with a specific cost of 1.8 €·kgH2−1. The carbon membranes prepared in this work are highly competitive with other separation processes for the recovery and purification of hydrogen from different industrial processes essential for the decarbonization.

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO2/N2 and CH4/N2 separation

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO2/N2 and CH4/N2 separation

The efficacy of carbon molecular sieve and solid amine for CO2 separation from a simulated wet flue gas by an internally heated/cooled temperature swing adsorption process

Considering that most sources of carbon dioxide (CO2) emissions are also waste heat sources, CO2 recovery using self–generated low–temperature waste heat is desirable. This study examines CO2 enrichment and recovery via a temperature swing adsorption (TSA) process. The low–temperature heating–driven TSA process requires an alternative regeneration method to conventional air heating to avoid dilution of the desorbed CO2, and to apply it to actual gas, using an adsorbent that does not lose its CO2 adsorption capacity because of coexisting water vapor is necessary. Zeolites tested in our previous study lose their CO2 adsorption ability under a humid feed gas and a low–temperature regeneration condition. For the former, efficacy of an internally heated and cooled adsorbent–packed fin–coil heat exchanger has been confirmed. This study thus attempts to overcome the latter issue by employing carbon molecular sieve (CMS) and solid–supported polyethyleneimine (PEI) as CO2 adsorbents. The effects of moisture in the inlet gas on the separation performance of adsorbents were investigated. The study reveals that PEI required moisture to extend for CO2 adsorption, and CO2 separation performance increased with higher humidity. PEI can produce the desorbed gas with a CO2 concentration of ∼ 45 % and a recovery ratio of ∼ 70 % from feed gas (CO2 concentration of ∼ 10 %) at a dew point temperature of 15 °C. Conversely, the CMS separation performance is almost independent of humidity. The desorbed gas of CMS indicates a CO2 concentration of only ∼ 30 % and a recovery of ∼ 30 %. The flow of the volumetric desorbed gases and the CO2 concentration rate indicates that CMS has the potential for reducing heat consumption by shortening the regeneration time because most of the CO2 desorbs during the early regeneration step. For increasing the concentration of recovered CO2, a severe control valve is required to eliminate the desorbed nitrogen (N2) accompanied by CO2. In contrast, CO2 desorption from PEI is slower than that in CMS, and PEI needs a relatively longer regeneration time.